The present invention relates to a handwritten character input device whose display position is correctable.
The conventional handwritten character input device, in which an electromagnetic induction tablet made of a transparent body is laid on or under an LCD or an EL display panel, has the following problems when characters are written with an input pen.
FIG. 5 shows a handwritten character input device with an electromagnetic induction tablet laid under an LCD.
Numeral 51 is an input pen and 52 is a transparent filter. The LCD 54 and the electromagnetic induction tablet 55 are spaced from transparent filter 52 by a predetermined gap 53. The gap 53 serves to prevent the transparent filter 52 from coming in contact with the LCD 54 in case the transparent filter 52 may be bent by the pen pressure of the input pen 51. When a character is handwritten with the input pen 51 on the pen-touch surface 52' of the transparent filter 52, magnetic flux from the input pen 51 is detected by the electromagnetic induction tablet 55 in term of coordinates. The dots corresponding to the coordinates are lit in succession so that a locus of the input pen 51 is displayed on the LCD surface 54'.
The tablet coordinate regions a', b' and c' correspond to the dots a, b and c of the LCD 54, respectively. When the input pen 51 is vertical with respect to the pen-touch surface 52' (as shown by (P) in FIG. 5), and if the electromagnetic induction tablet 55 detects the input as a coordinate "b'", then the dot "b" of the LCD 54 is turned on. When a person writes with the input pen 51, however, the input pen 51 is generally tilted at an angle .theta. from a line vertical to the pen-touch surface 52'. This tilting angle .theta. varies from person to person, ranging from 10.degree. to 40.degree.. If the input pen 51 is tilted to the right (as shown by (Q) in FIG. 5), the magnetic flux density distribution on the electromagnetic induction tablet 55 also deviates a little toward the right so that the input is detected as a coordinate "c'" by the electromagnetic induction tablet 55. As a result, the dot "c" is lit on the LCD 54. In contrast, if the input pen 51 is tilted to the left (as shown by (R) in FIG. 5), the magnetic flux density distribution on the electromagnetic induction tablet 55 deviates a little toward the left. Then, the input is detected as a coordinate "a'" and the corresponding dot "a" of the LCD 54 is lit.
FIG. 6 shows the magnetic flux density distributions on the electromagnetic induction tablet 55 for the positions (P), (Q) and (R) of the input pen 51.
Position (Q) is the position of the input pen 51 when it is held in the right hand, and (R) is the position of the pen 51 when it is held in the left hand. Thus, the position of the lit dot of the LCD 54 changes according to the tilting direction and angle of the input pen 51.
The position of the lit dot of the LCD 54 appears to be deviated from the eye position, as shown in FIG. 7. The same parts in FIG. 7 are indicated by the same reference numbers as in FIGS. 5 and 6. Suppose the input pen 51 is tilted at an angle .theta. toward the right so that the electromagnetic induction tablet 55 detects a coordinate "d'". The dot "d" of the LCD 54 directly under the pen point 51a of the input pen 51 should be lit corresponding to the detected coordinate "d'". If the operator's right eye right is over the pen point 51a, the pen point 51a is on the line 57 connecting the right eye with the dot "d" of the LCD 54. No deviation occurs.
Under the same condition, however, when viewed from the left eye, the result is different. In other words, the pen point 51a is not positioned on the line 59 connecting the eye with the dot "d" of the LCD 54. As a result, the dot "d" looks as if it deviated by a distance "f" from the pen point 51a. When viewed from the left eye, the dot right under the pen point 51a is the dot "e" which is positioned on the extension of the line 58 connecting the left eye and the pen point 51a.
This deviation is the result of a parallax caused by the distance 56 between the pen-touch surface 52' and the LCD surface 54'. Because of the parallax, the position of the lit dot of the LCD 54 looks as if it is deviated with respect to the pen point 51a by different amount depending upon the view position.
To be precise, refractions by the transparent filter 52 and the LCD 54 need to be taken into consideration. In FIG. 7, however, these are neglected for simplification.
Deviation along the X axis has been described above. The position of a lit dot of the LCD 54 also changes along the Y axis with the tilting angle of the input pen 51, or looks as if it deviated along the Y axis depending upon the view position with respect to the pen point 51a.